Which of the following is not an indication for treating a high frenum?

A high maxillary frenum with a sufficient band of attached gingiva is not an indication for treatment because the presence of attached gingiva indicates that there is adequate tissue to support the health of the periodontal structures in that area. If the frenum is high but there is still an adequate band of attached gingiva, it typically does not contribute to any clinical issues like inflammation or recession.

In contrast, when a high frenum attachment is associated with persistent gingival inflammation or progressive recession, these situations warrant treatment as they can lead to further periodontal problems. Similarly, a high frenum with an associated midline diastema is another situation that may require intervention due to its potential effects on aesthetics and function, as well as the possibility of exacerbating tooth movement or spacing issues. Therefore, the presence of a sufficient band of attached gingiva alleviates the need for treatment related to the frenum, making it the correct choice as not being an indication for treatment.